Rebuild Redis, Git, and SQLite
from scratch.
Real-systems programming challenges for senior engineers. Code in your IDE, push with git, master the fundamentals tutorials skip.
Free to start · Use your own IDE · No setup required
Enjoyed by developers at the world's best companies:
Simple by design
Pick a challenge, open your editor, git push to test. That's it.
Redis, Git, SQLite, and 8 more real systems
Your IDE, your extensions, your terminal. No toy editors
git push to run tests. Results and hints in seconds
Redis, Git, SQLite, and 8 more real systems
Your IDE, your extensions, your terminal. No toy editors
git push to run tests. Results and hints in seconds
Rebuild the software you use every day
11 challenges that take you inside the architecture of real systems.
No toy projects. No algorithm drills.
Learn about parsing shell commands, executing programs and more
Learn about TCP servers, the Redis protocol and more
Learn about LLM APIs, tool calling, agent loops and more
Learn about regular expressions, pattern matching and more
We strive to provide a proper workout. You won't become a great swimmer by watching the Olympics on YouTube.
Developers love CodeCrafters
Here’s what they say after trying our challenges:
Djordje Lukic
Docker contributor
These guys ruined my weekend
Charles Guo
Scala Team at Stripe
The Redis challenge was extremely fun. I ended up having to read Redis protocol specification doc pretty carefully in its entirety! The result felt like lightly-guided independent study, if that makes sense. (Which, again, was lots of fun)
Cindy Wu
Engineering at Vercel
I've started the SQLite challenge, enjoying it a lot so far. Just the right level of guidance, helpful yet gives you a lot of freedom to explore and learn for yourself.
Raghav Dua
SRE at Coinbase
I spent a full day on your course and ended up building the whole thing myself. As a SRE (and mostly a user of SQLite), digging into the internals blew me away.
Djordje Lukic
Docker contributor
These guys ruined my weekend
Ananthalakshmi Sankar
Engineer at Apple
There are few sites I like as much that have a step by step guide. The real-time feedback is so good, it's creepy!
Raghav Dua
SRE at Coinbase
I spent a full day on your course and ended up building the whole thing myself. As a SRE (and mostly a user of SQLite), digging into the internals blew me away.
Rahul Tarak
Pioneer.app & ODX1 Fellow
The Redis challenge was a great way to procrastinate sleeping for a week! A good change of pace from my regular work, and allowed me to explore some cool tech. I'll be back for more.
Charles Guo
Scala Team at Stripe
The Redis challenge was extremely fun. I ended up having to read Redis protocol specification doc pretty carefully in its entirety! The result felt like lightly-guided independent study, if that makes sense. (Which, again, was lots of fun)
Akshata Mohan
Sr. Data Scientist at Cloudflare
I'm learning about how Redis works under the hood, system calls, socket programming in Python; something I've never done before
Cindy Wu
Engineering at Vercel
I've started the SQLite challenge, enjoying it a lot so far. Just the right level of guidance, helpful yet gives you a lot of freedom to explore and learn for yourself.
Pranjal Paliwal
Winner of HackAtom
My favorite way to master a language.
Vladislav Ten
SWE at Microsoft
In a perfect world, job interviews ask for assignments like CodeCrafters instead of Leetcode. The best way to refresh your programming language skills and learn something new about Redis, Git, SQLite internals.
Kang Ming Tay
SWE at Supabase
The challenge helped me dive into its internals, through *actual* practice. Super fun.
Jonathan Lorimer
Senior SWE at Mercury
I was really impressed that they support Haskell, and will probably use this to learn Rust! The git-based workflow is 👨🍳
Beyang Liu
CTO at Sourcegraph
Found out from a colleague. It has you build your own version of things like Git and SQLite from scratch. A cool way to build a stronger mental model of how those tools work.
The world's most
advanced projects
Implement a Redis from scratch. Parse Git objects. Write your own SQLite. Each challenge drops you into exploring storage engines, network protocols, binary formats.
Once you’ve written and read code around these topics, everything else tends to feel easy.
CodeCrafters has been a fantastic resource in helping me maintain my skills in a pragmatic fashion, learn about new areas, and even new languages.
Howard Lee
Principal Software Engineer, Okta
The world's most
experienced users
See how contributors to projects like Redis and Rails refactor, how engineers who build large-scale systems debug, and how CTOs of developer platforms make architectural decisions.
Improve your taste by observing other great engineers.
This idea is absolutely stellar. Having a structured project like this feels like a blast.
Joey Pereira
Software Engineer at OpenAI
The world's most
advanced tooling
Don’t be limited by web-based editors. Code in your usual IDE, with your preferred customisations. Push code with Git and get instant feedback. Share your work on GitHub.
CodeCrafters is designed for pros.
There are few sites I like as much that have a step by step guide. The real-time feedback is so good, it's creepy!
Ananthalakshmi Sankar
Engineer at Apple
The world's most
advanced projects
Implement a Redis from scratch. Parse Git objects. Write your own SQLite. Each challenge drops you into exploring storage engines, network protocols, binary formats.
Once you’ve written and read code around these topics, everything else tends to feel easy.
CodeCrafters has been a fantastic resource in helping me maintain my skills in a pragmatic fashion, learn about new areas, and even new languages.
Howard Lee
Principal Software Engineer, Okta
This idea is absolutely stellar. Having a structured project like this feels like a blast.
Joey Pereira
Software Engineer at OpenAI
There are few sites I like as much that have a step by step guide. The real-time feedback is so good, it's creepy!
Ananthalakshmi Sankar
Engineer at Apple